1. Field of the Invention
The invention relates to a method of transmitting digital data in which digital data is retained in sectors each comprising a plurality of sync frames and sequentially transmitting it (including recording of the digital data).
2. Description of Background Information
As an RLL (Run Length Limited) encoding method which is performed in order to transmit digital data indicative of information or record the digital data to a recording medium, an EFM (Eight to Fourteen Modulation) which is used for a CD (compact disc) or the like is known.
In the EFM, digital data of eight bits (one byte) is converted to a run length limed code of 14 bits which satisfies run length limitations of:                minimum run length d=2T;        maximum run length k=10T;connection bits of three bits are added to intervals among the respective converted data, and the resultant data is formed as an EFM modulation signal. In a sequence of the EFM modulation signals as well, a bit rain of the connection bits is set so as to satisfy the foregoing run length limitation.        
In the CD, a signal obtained by adding a sync signal to the EFM modulation signal has been recorded. The sequence by the EFM modulation signals is constructed in a manner such that a repetitive pattern of maximum interval which corresponds to the maximum run length k, namely, repetitive pattern such as 11T-11T doesn't exist in the sequence and the repetitive pattern of 11T is used as a sync signal.
In a CD player, the sync signal is extracted by detecting the repetitive pattern of 11T from a signal read out from the CD.
In a DVD (digital video disc) in which recording information has been recorded at a high density or a high-density data transmission, however, when reading the information, it is largely influenced by an inter-symbol interference. The repetitive pattern of 11T as a sync signal is, therefore, changed to a pattern such as 11T-10T or 10T-11 and is read out. On the contrary, a case where the data pattern such as 10T-11T or 11T-10T as an EFM modulation signal is changed to the repetitive pattern of 11T and is erroneously detected as a sync signal occurs.
As mentioned above, in the high-density recording or high-density data transmission, a frequency of errors which occur in the detection of the sync signal increases and a burst error due to out-of-synchronism easily occurs.